1. Field of the Invention
The present invention relates to a Westco-type pump, which is suitable, for example, as an automobile fuel pump. The "Westco-type pump" referred herein is also called a vortex pump, a regenerative pump or a periphery pump.
2. Related Art Statement
The Westco-type pump makes use of an impeller which is a disk formed on its entire periphery with a multitude of recesses. A pumping action is effected in a working passage surrounding a portion of the periphery of the impeller. One end of the working passage is communicated via an intake passage with a suction tube and the other end is communicated via a discharge passage with a discharge tube. There is a partition between the discharge passage and the intake passage. There is formed an extremely small radial space between an outer periphery of the impeller and an inner periphery of the partition, and an extremely small axial space (a side clearance) between a radial inward end surface portion of the impeller and a radial inward inner surface portion of a casing.
According to the conventional Westco-type pump, when the side clearance between the impeller and the casing is reduced, the pumping efficiency is increased because the leakage of the fluid is reduced. On the other hand, however, there is a possibility that a linking phenomenon occurs in which the impeller and the casing adhere to each other. The "linking phenomenon" is explained as follows. A strong force is required to separate two surfaces which are close to each other when such surfaces are machined at high flatness, since there is no flow of fluid therebetween. This phenomenon can occur between the impeller and the casing of the pump. When the linking phenomenon takes place, the sliding resistance is substantially increased and then the pumping efficiency is deteriorated. For this reason, there has hitherto been a limitation to reduce the side clearances between the impeller and the casing.
In order to resolve this problem, several efforts have been made heretofore. For example, Japanese Unexamined Patent Publication No. 58-19745 discloses a recess provided in an inner surface of the casing for generating an axial force urging the impeller, thereby improving the pumping efficiency. Japanese Unexamined Patent Publication No. 58-2495 discloses a spiral groove formed on an end surface of the impeller so as to reduce the thrust load acting on the impeller. Japanese Unexamined Utility Model Publication No. 57-114195 discloses a number of spiral grooves formed on an end surface of the impeller and an inner surface of the casing. Further, Japanese Unexamined Patent Publication No. 60-85284 discloses a wedge-shaped layer formed between an inner wall of the housing and a sliding surface of the impeller, thereby reducing the wear of the impeller.
However, the impeller configurations according to these prior art devices are incapable of producing a sufficiently uniform fluid film in the side clearance formed between an end surface of the impeller and an inner surface of the housing and does not significantly suppress the generation of the linking phenomenon. Especially, in case that the spiral grooves are formed on the end surface of the impeller, an unbalance of the fluid is positively created within the seal surface region so that the impeller tends to incline due to a slight pressure difference or the like.